A caster assembly is a wheel or a set of wheels mountable in a suitable frame, such as, e.g., a clevis-type or a U-shaped frame. The frame is free to swivel about a generally vertical axis, i.e., the castering axis, which is perpendicular to the axis of a rotation of the wheel but offset therefrom to create an eccentricity. Freedom of movement about the castering axis and a proper eccentricity allows a caster assembly to be self-steering, i.e., the assembly will move in the direction of a motive force or a steering force. Caster assemblies are typically used in supporting relatively light loads such as, e.g., furniture, or relatively heavy loads such as, e.g., trucks and various portable machines.
In reversing the direction and thus the eccentricity of a conventional caster assembly, its caster wheel must rotate or swivel 180.degree. about the castering axis inducing lateral movement of the assembly and consequently any load being supported. This swiveling of the caster wheel requires additional force and motion which may be undesirable under certain circumstances. Furthermore, highly loaded caster wheels do not rotate very easily about the castering axis.
Certain caster assemblies are linearly reversible, i.e., the caster wheels need not swivel about the castering axis as the eccentricity of the assembly is changed thereby allowing the load carried by the assembly to be readily moved in a forward or a reverse direction. Such assemblies are exemplified by U.S. Pat. No. 1,829,396 issued Jan. 5, 1932 to Kimball and U.S. Pat. No. 1,343,758, issued June 15, 1920 to Austin.
Unfortunately, the caster assembly of Kimball induces frictional forces tending to preclude reliable rectilinear reversal of the motion of the caster wheel. Under such circumstances, there may be some lateral movement of the caster assembly making it difficult to roll the loaded caster assembly out of constrained locations.
The caster assembly of Austin causes the load supported by the assembly to be slightly elevated as the caster wheel reverses direction which may be undesirable under certain circumstances. Also, the frictional forces associated with the Austin assembly may preclude linear reversal of its caster wheel.
Finally, neither the caster assembly of Kimball nor the caster assembly of Austin appears to be intended to support heavy loads. Where reliability of reversal, rectilinear translation of the load during reversal and high load-carrying capabilities are required, prior art caster assemblies, represented by Kimball and Austin, may be inadequate.